1. Field of the Invention
This invention relates to a thermal image transfer system, comprising a sublimation type thermal image transfer recording medium in combination with an image receiving medium comprising a substrate and a dye receiving layer formal thereon, the dye receiving layer comprising, as the principal components, a vinyl chloride-based resin containing active hydrogens and an isocyanate compound.
2. Discussion of Background
Recently the demand for full color printers is increasing year by year. Typical recording methods for full color printers now available include the electrophotographic method, the ink-jet method, and the thermosensitive image transfer method. Of these methods, the thermosensitive image transfer method is most widely employed because of its advantages over the other methods in that the maintenance is easy and the operation is noiseless.
In the thermosensitive image transfer recording method, a solidified color ink sheet and an image receiving sheet are employed, and a color ink is transferred imagewise from the ink sheet to the receiving sheet by the thermal fusion or the sublimation of the ink, under the application of thermal energy by laser beams or a thermal head which is controlled by electric signals.
Thus, the thermosensitive image transfer recording method can be roughly classified into two types, a thermal fusing image transfer type and a sublimation image transfer type. The sublimation image transfer type is advantageous over the thermal fusing type in that halftone can be obtained without difficulty and image gradation can be controlled as desired. These benefits exist because a sublimable dye is in principle sublimated in the form of independent molecules in such an amount as to correspond to the amount of thermal energy applied thereto, for instance, through a thermal head. Therefore, the sublimation image transfer type is considered the most suitable for color printers.
As the sublimation image transfer recording method, there have been known (i) an n-times use mode recording method in which the running speed of the image receiving sheet is made n (n&gt;1) times the running speed of the ink sheet when images are recorded, (ii) an area-sequential recording method which uses a line head and (iii) a line-sequential recording method which uses a serial head as a thermal head.
Hitherto, there has been employed, in the sublimation-type thermal image transfer recording method, an image receiving sheet which consists of a substrate (paper, synthetic paper, plastic film, etc.) and a dye receiving layer formed thereon containing as its main component a thermoplastic resin, such as polyester resin, which can be well dyed with a sublimation-type dye.
The above image receiving sheet, however, cannot be smoothly released from the ink sheet after the thermal image transfer recording is completed. Especially, when the n-times use mode recording method is employed, the ink sheet and the image receiving sheet are strongly frictionized each other when images are recorded, so that these two sheets tend to stick to each other or to be damaged.